Q2 50-74

Question 1

Assuming that you are running a Bourne-shell and the abc file does not exist, what is the output of the following Unix commands: 
cd /tmp;
pwd > abc; 
ln abc ABC;
rm abc;
cat ABC

Answer 1

1. Bring us to /tmp folder
2. Write a new file abc with our pwd, /tmp
3. Link abc to ABC
4. Removes the original abc file
5. Cannot open ABC, because the file it’s hard linked to has been removed

Question 2

Predict the output of the following commands:
   cd ~
   pwd
   tcsh
   cd /
   pwd
   exit
   pwd

Answer 2

1. Change Directories to the user’s home directory
2. Show our Present Working Directory
3. Change our shell to C shell (tcsh)
4. Change Directories to absolute root
5. Show our Present Working Directory
6. Exit C shell
7. We will now be back at our user’s home directory (cd ~) because changing shells doesn’t affect our pwd.

Question 3

In tcsh shell, how do you create a regular variable?

Answer 3

set varname = variable

Question 4

In sh shell, how do you create a regular variable?

Answer 4

varname = variable

Question 5

In tcsh shell, how do you change a value of a regular variable?

Answer 5

set varname = newVariable

Question 6

In sh shell, how do you change a value of a regular variable?

Answer 6

varname=newVariable

Question 7

In tcsh shell, how do you delete a regular variable?

Answer 7

unset varname

Question 8

In sh shell, how do you delete a regular variable?

Answer 8

unset varname

Question 9

In tcsh shell, how do you create an environment variable?

Answer 9

setenv environmentVarname environmentVariable

NO EQUAL SIGN

Question 10

In sh shell, how do you create an environment variable?

Answer 10

environmentVarname=EnvironmentVariable

export EnvironmentVarname

Question 11

In tcsh shell, how do you change a value of an environment variable?

Answer 11

setenv environmentVarname newEnvironmentVariable

Question 12

In sh shell, how do you change a value of an environment variable?

Answer 12

unset environmentVarname
environmentVarname=newEnvironmentVariable
export EnvironmentVarname

Question 13

In tcsh shell, how do you delete an environment variable?

Answer 13

unsetenv environmentVarname

Question 14

In sh shell, how do you delete an environment variable?

Answer 14

unset environmentVarname

Question 15

What is the difference between regular shell variables and environment shell variables?

Answer 15

Global/Environmental affects the current shell and all the programs invoked from that shell.

Local/Regular affects only the current shell but none of the shell it invokes.

Question 16

In tcsh shell, how do you display all current environment variables?

Answer 16

env

Question 17

In tcsh shell, how do you display all current regular variables?

Answer 17

set

Question 18

In sh shell, how do you display all current environment variables?

Answer 18

env

Question 19

In sh shell, how do you display all current regular and environment variables?

Answer 19

set

Question 20

Is there a command under sh shell that can display current environment variables alone?

Answer 20

printenv

Question 21

In tcsh shell, create an alias named rm that always deletes files recursively.

Answer 21

alias remove rm -r -f

Question 22

In tcsh shell, create an alias named ls that always display files with long format.

Answer 22

alias long ls -l

Question 23

In tcsh shell, how would you configure the Unix history to store the last 200 commands?

Answer 23

set history=200

Question 24

In tcsh shell, how would you configure the Unix history to store the last 100 commands between two consecutive sessions?

Answer 24

set savehist=100